Preheat oven to 350°. Prepare cornbread mix according to package directions. Let cool 30 minutes; crumble into a large bowl.
Meanwhile, pick crabmeat, removing any bits of shell.
Melt butter in a large skillet over medium heat; add celery and onion, and sauté 10 to 12 minutes or until tender. Stir in 1/2 tsp. Old Bay seasoning. Stir celery mixture, crab, bread cubes, parsley, and lemon zest into crumbled cornbread, stirring gently until blended. Add broth, and stir gently until moistened.
Sprinkle cavity of fish with remaining 1/2 tsp. Old Bay seasoning. Spoon stuffing mixture into fish, and secure with kitchen string. Place fish in a large, lightly greased roasting pan.
Bake at 350° for 45 to 50 minutes or until fish flakes with a fork.